1. Field of the Invention
The present invention relates to a nonreciprocal circuit device and a communication apparatus including such a nonreciprocal circuit device.
2. Description of the Related Art
In general, a nonreciprocal circuit device includes a permanent magnet, a center electrode assembly to which a DC magnetic field is applied by the permanent magnet, a metallic case that accommodates the permanent magnet and the center electrode assembly, and matching capacitors electrically connected to the center electrode assembly.
In related nonreciprocal circuit devices, the pass characteristic and the reflection loss were regarded as important matters, and these devices were designed so that, at the center frequency in a pass band, the insertion loss was at a minimum value and the input/output reflection losses became a maximum value. On the other hand, the impedance of the nonreciprocal circuit device from the input terminal side (hereinafter referred to as xe2x80x9cinput impedancexe2x80x9d) was regarded as an important matter compared with the pass characteristic and the reflection characteristic, and the standard of the input impedance was hardly considered in the design. That is, in the related nonreciprocal circuit devices, an electronic capacitance of the matching capacitors was set so that, the insertion losses became the minimum value at the frequency as well as the input/output reflection losses became the maximum value thereof, and consequently, the input impedances thereof were automatically set.
When the related nonreciprocal circuit device designed as described above was included in a communication apparatus such as a portable telephone, impedance matching between the nonreciprocal circuit device and a next-stage electric circuit might not be achieved. It was therefore, necessary to adjust the input impedance of the nonreciprocal circuit device by changing the electrostatic capacities of the matching capacitors thereof in order to achieve impedance matching. However, when the input impedance of the nonreciprocal circuit device was adjusted, the frequency at which the input-side reflection loss became the maximum value deviated significantly from the center frequency, and consequently, the frequency at which the insertion loss became the minimum value also deviated significantly from the center frequency, whereby a specification that a customer demanded might not be satisfied.
In order to overcome the problems described above, preferred embodiments of the present invention provide a nonreciprocal circuit device and a communication apparatus that allow the input impedances to be set at desirable values without changing the characteristics of the inner components and that satisfy the required insertion loss.
According to a preferred embodiment of the present invention, a nonreciprocal circuit device includes a first frequency at which the input-side reflection loss becomes a maximum value is set to be lower or higher than the center frequency in a pass band, a second frequency at which the output-side reflection loss becomes a maximum value is set to be higher or lower than the center frequency, the center frequency is located between the first frequency and the second frequency.
More specifically, the present invention provides a nonreciprocal circuit device that includes a permanent magnet, a center electrode assembly which has a ferrite member, and a plurality of center electrodes disposed on the surface of the ferrite member so as to cross each other at predetermined angles, and to which a DC magnetic field is applied by the permanent magnet, a metallic case that has the permanent magnet and the center electrode assembly disposed therein, matching capacitors electrically connected to the center electrode assembly, and by adjusting the electrostatic capacitance of the matching capacitors, or by adjusting the crossing angles between the center electrodes, a first frequency at which the input-side reflection loss becomes a maximum value is set to be lower or higher than the center frequency in a pass band, a second frequency at which the output-side reflection loss becomes a maximum value is set to be higher or lower than the center frequency, the center frequency is located between the first frequency and the second frequency.
With these characteristics, when input impedance matching of the nonreciprocal circuit device is to be performed, the electrostatic capacities of the matching capacitors or the crossing angles between the center electrodes are appropriately adjusted so that the center frequency in a pass band is located between the frequency at which the input-side reflection loss becomes the maximum value and the frequency at which the output-side reflection loss becomes the maximum value. Thereby, the frequency at which insertion loss becomes the minimum value is close to the center frequency, thereby satisfying the insertion loss standard.
Also, the communication apparatus according to another preferred embodiment of the present invention, which is equipped with the nonreciprocal circuit device having the above-described features, achieves greatly improved impedance matching between the nonreciprocal circuit device and a next-stage electric circuit, and has a reduced power consumption.
Other features, elements, characteristics and advantages of the present invention will become more apparent from the following detailed description of preferred embodiments of the present invention with reference to the attached drawings.